AMMAN, Jordan – Jordan sealed its last entry point for Syrian refugees Tuesday after a cross-border suicide attack killed six members of the Jordanian security forces, wounded 14 and exposed the pro-Western kingdom's growing vulnerability to spillover from conflict next door.
The closure raised questions about the fate of tens of thousands of Syrian refugees who are stranded in remote desert areas along the border, many of them for months, and depend on daily deliveries of food and water from the Jordanian side.
Jordan said its security comes first. Government spokesman Mohammed Momani said Jordan had warned for months that militants, including those from the Islamic State group, are mingling with refugees in the two rapidly expanding encampments on the border and pose a serious security threat.
"The border will be closed," Momani told reporters. "We will not allow the crossing of people or vehicles through that area."
King Abdullah II said in a statement that Jordan will "respond with an iron fist" to anyone harming its borders or security, but did not lay out specifics.
There was no immediate claim of responsibility for the assault, the third against Jordanian security installations in seven months.
Tuesday's attack was launched at dawn near Ruqban, the larger of the two border camps.
The assailant drove a truck packed with explosives at high speed through an opening in the border, said Momani. "It reached our side of the border and it ended up exploding with the driver inside," he said.
The military said the blast targeted a Jordanian army post.
A Ruqban resident said he saw a pickup truck crashing through a Jordanian border gate. Seconds later, a blast went off, followed by the sound of shooting, said the resident, who spoke to The Associated Press over the phone from the area. He spoke on condition of anonymity for fear of repercussions from the authorities.
Cellphone photos from the camp show a cloud of gray smoke rising in the distance, with tents in the foreground.
Ruqban and the smaller Hadalat camp house about 64,000 Syrians, according to estimates by international aid agencies. The camps have also attracted smugglers, war profiteers and members of various armed groups fighting in Syria's civil war.
The camps are located between two berms, or earthen barriers, that run parallel to the border, which is not clearly marked in the area. Ruqban is just a few miles from the point where Syria, Jordan and Iraq meet.
In recent weeks, international agencies stepped up deliveries of water, food and medical care for refugees at the berm. Aid workers set up makeshift delivery points on the Jordanian side every day and refugees climbed over the berm to pick up food parcels, get first aid or register with the U.N. refugee agency.
The arrangement kept aid workers and Jordanian troops out of the camps for security reasons. Instead, Jordanian troops stood on top of the southern berm to monitor distributions, firing tear gas or shooting in the air if order broke down.
In recent weeks, aid agencies had won Jordan's agreement to set up more prefab trailers in the area to improve distribution and refugee registration.
Momani said Tuesday that those plans were now on hold.
Instead, "we will be discussing ways through which we can send aid to the people on the other side of the border," he said, adding that details would be worked out by the U.N. refugee agency and the Jordanian military.
He did not elaborate. It's not clear how long refugees in the encampments can hold out without daily aid shipments.
The U.N. refugee agency said it is aware of heightened security restrictions, but will seek to provide continued support to the refugees. "A key issue will be to ensure the continued provision of water to this desolate location, given the inhospitable environment," said spokesman Andreas Needham in Geneva.
Even before the attack, conditions in the camps were deteriorating. Refugees are exposed to the extreme desert climate and mounds of garbage grow by the day.
Jordan has restricted admissions of refugees from the berm, citing the need for security vetting. In recent weeks the pace picked up, from a few dozen admissions a day to about 300, as part of a promise to the U.S. to let in 20,000 displaced Syrians.
The kingdom already hosts more than 655,000 Syrian refugees, out of more than 4.8 million who have fled a brutal civil war, now in its sixth year.
Momani said Jordan does not know who is behind the attack, but that "we have strong evidence of the presence of terrorist elements and Daesh elements in that group (of refugees)." Daesh is an Arabic acronym for the Islamic State group.
Jordan is a member of the U.S.-led military coalition fighting IS, and has fortified its border defenses, including with U.S.-funded surveillance systems.
At the same time, Jordanian officials have played down concerns that militant groups, including IS, pose an external and internal threat to the kingdom.
In Washington, State Department spokesman John Kirby condemned the attack, expressed "unwavering" U.S. support for the Jordanian military and praised the kingdom for its "determination in dealing with the threat posed by Daesh."
"We'll continue to cooperate closely in the wake of this attack," he said.
Jordan has also widened a crackdown on IS sympathizers at home, jailing hundreds in the past two years for promoting the group's ideas on social media.
Jordanian security installations were targeted twice before in the past seven months.
In November, a Jordanian police captain opened fire on instructors at an international police training center in the capital, Amman, killing five people, including two Americans, before being shot dead by security forces.
Two weeks ago, a gunman armed with an assault rifle killed five people in an office of Jordan's intelligence agency. The assailant, said to have previous ties to Islamic militant groups, was arrested several hours later. The government said he was a lone wolf and imposed a gag order, preventing further reporting.